Maybe this was a test by their team or something to see how well a large transaction would work.  The government has come out and said that they can trace coins through traditional coin mixers if the amount is over a certain threshold.  Perhaps this is them testing if they can truly keep large transactions anonymous.  It also could just be a promotional tactic.  I've seen plenty of posts and articles about this large transaction already, which is probably the best advertising one could have for Wasabi wallet.  I think that's more likely then someone suddenly wanting to use coinjoin for such a massive transaction.  Even if they were to use coinjoin for this amount, wouldn't they still split it up to avoid being in the news? Seems contrary to what they were trying to accomplish if it were a real transaction.